Traditional UV-Oxidation (UV/Ox) systems employ a UV lamp inside of a quartz sleeve installed in an annular reactor. This style of reactor is widely known. The quartz sleeve protects the UV lamp from the wastewater; however, during treatment, the quartz sleeve typically gets fouled with metal and other oxide layers. This coating absorbs the UV light and thus should be cleaned for optimal use.
In the past, various forms of wiper mechanisms have been designed to remove these layers from a quartz sleeve. All such forms of wiper mechanisms act to ‘wipe off’ the oxide layer from the external surface of the sleeve. Unfortunately, such wiper mechanisms suffer from a number of drawbacks, including the fact that they are typically large complicated devices that require a large annular space between the outside surface of the sleeve housing the UV lamp and the surrounding tubing housing the sleeve in order to accommodate the wiper mechanism. UV/Ox systems rely on the transmissivity of the water in order to allow the UV photons to reach the contaminants in the fluid passing through the annular region between the sleeve and housing. However, as the size of the annular region between the sleeve and tubing surrounding the sleeve increases, the effectiveness of the UV light at the outer edges of the annulus region decreases, which often impacts the efficiency of the system. In addition, conventional wiper mechanisms contain a number of moving parts that are submersed in water, thus raising reliability concerns. Also, such wiping mechanisms can etch the surface of the quartz sleeve during the wiping action, which may result in premature failure of the sleeve. Furthermore, some wiper mechanisms employ acidic solutions in the cleaning process, thus raising corrosion issues.
Prior techniques employed to overcome the need for wipers is provided by the photocatalytic treatment of contaminated media, such as discussed in U.S. Pat. No. 5,462,674, which is commonly assigned with the present disclosure and incorporated herein by reference for all purposes. Specifically, the use of photocatalysts in such a system typically provides a continuous cleaning benefit for the quartz sleeves. However, there are some treatment applications where there is minimal or no benefit to using photocatalysis over a photolysis treatment that occurs in typical treatment systems. Thus, employing a photolytic system over a photocatalytic system is far more cost effective since the need for photocatalyst recovery equipment and the like is not required. One example is the treatment of nitrosodimethylamine (NDMA), which is a contaminant that is destroyed solely by UV light (i.e. 200 nm-270 nm). Utilizing a photocatalytic mode of treatment for NDMA is not optimal since it does not increase destruction efficiency over photolysis, but yet requires additional cost for a catalyst recovery operation.
The same cost benefit analysis may hold true for many other organic or inorganic contaminant that is easily photolyzed. Another example with little or no benefit of operating a photocatalytic system over the typical photolytic process is in UV-disinfection. Once again, it is the UV light energy that performs the work, and thus the addition of a photocatalyst (and additional equipment) does little or nothing for system efficiency, while still adding an additional catalyst recovery operation (and cost) to the process. Unfortunately, however, when switching from a photocatalytic system to a more cost effective photolytic system, the lack of the photocatalyst typically results in a build-up of contaminated and other residue on the outer surface of the quartz sleeves housing the UV lamps used in the photolytic process, thus necessitating the wiper mechanisms discussed above. Accordingly, what are needed in the art are systems and methods for cleaning the sleeves housing the UV lamps in UV decontamination systems that do not suffer from the deficiencies associated with conventional techniques.